A case report of severe digitalis poisoning in a patient with prosthetic heart valve is presented. He complained of nausea, vomiting, drowsiness, temporal disorientation and lethargy. The electrocardiogram showed idioventricular rhythm, and plasma levels of digoxin were 6.78 ng/ml. Predisposing factors por digitalis poisoning were prerenal failure and concomitant quinidine therapy. Treatment with digoxin-immune antibody fragments (FAB) promptly lead to abolition of the ventricular arrhythmia and disappearance of every clinical symptoms in hours. Plasma digoxin levels showed a steep decrease until normal values at the fifth day. The favourable course of either clinical and electrocardiographic response to IV administration of FAB are discussed, stressing the fact of the high morbidity of digitalis poisoning in opposition to the relative safety of Fabs use in its therapy.